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Ecology and Epidemiology

Frequency, Distribution, and Characteristics of Endophytic Pseudomonas syringae in Pear Trees. S. K. Whitesides, Postdoctoral research associate, Oregon State University, Mid-Columbia Agricultural Research and Extension Center, Hood River, OR 97031; R. A. Spotts, professor, Oregon State University, Mid-Columbia Agricultural Research and Extension Center, Hood River, OR 97031. Phytopathology 81:453-457. Accepted for publication 20 November 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-453.

Internal stem and root tissues of pear trees were sampled for presence of Pseudomonas syringae at seven orchards in Oregon. Isolates positive for fluorescence (F+) and negative for cytochrome oxidase reaction (Ox—) were defined as P. syringae. Endophytic F+ Ox— strains occurred in 84% (57/68) of the trees. Eighty-one percent (191/235) of the F+ endophytic stains were Ox—. A total of 159 and 32 P. syringae strains were found in root and stem tissues, respectively. The endophytic P. syringae strains varied with respect to ice nucleation activity, induction of hypersensitive response on tobacco, pathogenicity on pear and cherry fruitlets, and genomic DNA fingerprinting. Inoculations of P. syringae into root and stem tissues of potted trees resulted in detectable but limited bacterial movement up to 3.0 cm in stems and no detectable movement above the crown from root inoculations.